Pregnancy Due Date Calculator

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Pregnancy Due Date Calculator
Last Menstrual Period (LMP)Conception DateIVF Transfer Date
Day 3 EmbryoDay 5 Embryo
Estimated Results:
Enter your information and click Calculate
function toggleInputs(){var method=document.getElementById('calc_method').value;var labelDate=document.getElementById('label_date');var rowCycle=document.getElementById('row_cycle');var rowIvf=document.getElementById('row_ivf');if(method==='lmp'){labelDate.innerHTML='First Day of LMP:';rowCycle.style.display='table-row';rowIvf.style.display='none';}else if(method==='conception'){labelDate.innerHTML='Date of Conception:';rowCycle.style.display='none';rowIvf.style.display='none';}else if(method==='ivf'){labelDate.innerHTML='Transfer Date:';rowCycle.style.display='none';rowIvf.style.display='table-row';}}function calculateDueDate(){var method=document.getElementById('calc_method').value;var dateVal=document.getElementById('input_date').value;if(!dateVal){alert('Please select a date');return;}var baseDate=new Date(dateVal);var dueDate=new Date(baseDate);var conceptionDate=new Date(baseDate);var cycle=parseInt(document.getElementById('cycle_length').value)||28;if(method==='lmp'){dueDate.setDate(baseDate.getDate()+280+(cycle-28));conceptionDate.setDate(baseDate.getDate()+(cycle-14));}else if(method==='conception'){dueDate.setDate(baseDate.getDate()+266);conceptionDate=new Date(baseDate);}else if(method==='ivf'){var ivfType=parseInt(document.getElementById('ivf_type').value);dueDate.setDate(baseDate.getDate()+(266-ivfType));conceptionDate.setDate(baseDate.getDate()-ivfType);}var today=new Date();var diffDays=Math.floor((today-conceptionDate.getTime()+(14*24*60*60*1000))/(24*60*60*1000));var weeks=Math.floor(diffDays/7);var days=diffDays%7;var html='
Your Estimated Due Date:
'+dueDate.toLocaleDateString('en-US',{weekday:'long',year:'numeric',month:'long',day:'numeric'})+'
';html+='
Current Progress: '+weeks+' weeks, '+days+' days
';if(document.getElementById('show_milestones').checked){var t1=new Date(conceptionDate);t1.setDate(conceptionDate.getDate()+(12*7)-14);var t2=new Date(conceptionDate);t2.setDate(conceptionDate.getDate()+(27*7)-14);html+='

Important Milestones:

';html+='';html+='';html+='';html+='
End of First Trimester:'+t1.toLocaleDateString()+'
End of Second Trimester:'+t2.toLocaleDateString()+'
Approx. Conception Date:'+conceptionDate.toLocaleDateString()+'
';}document.getElementById('answer').innerHTML=html;}

Calculator Use

The pregnancy due date calculator is a professional-grade tool designed to estimate the date of delivery for expectant parents. By using standard obstetric methods, this tool helps you plan for your new arrival and track significant milestones throughout your pregnancy journey.

To get the most accurate result, you can choose from three different calculation methods based on the information you have available. Whether you know the exact day of conception or only the first day of your last period, this calculator provides a reliable estimate.

Last Menstrual Period (LMP)
This is the most common method used by healthcare providers. It assumes pregnancy lasts 280 days from the first day of your last period.
Average Cycle Length
The default is 28 days. Adjusting this helps refine the calculation for those with shorter or longer cycles, as ovulation usually occurs 14 days before the next period starts.
Conception Date
If you tracks ovulation or know the exact date of conception, the calculator adds 266 days to that date to find the due date.

How It Works

Most pregnancies last approximately 40 weeks (280 days) from the first day of the last menstrual period. The pregnancy due date calculator uses Naegele's Rule as a baseline, but applies adjustments for specific cycle lengths or conception dates.

Due Date = LMP + 280 Days + (Cycle Length – 28 Days)

  • LMP: The start of your pregnancy journey in clinical terms.
  • Cycle Adjustment: If your cycle is 30 days, you likely ovulated two days later than the average woman, so two days are added to the due date.
  • Trimesters: The calculator divides the 40 weeks into three blocks to help you track developmental stages.

Calculation Example

Example: Let's say your Last Menstrual Period began on January 1st, and you have a regular 30-day menstrual cycle.

Step-by-step solution:

  1. LMP = January 1, 2024
  2. Standard 40-week addition (280 days) = October 7, 2024
  3. Cycle adjustment (30 days – 28 days) = +2 days
  4. Final Due Date = October 9, 2024
  5. Estimated Conception = January 1 + (30 – 14) = January 17, 2024

Common Questions

How accurate is the due date?

A due date is only an estimate. Only about 4% of babies are born on their exact due date. Most babies arrive between 37 and 42 weeks of pregnancy. The pregnancy due date calculator provides a target, but your doctor may adjust this date based on early ultrasound measurements.

Why is the pregnancy 40 weeks if gestation is 9 months?

Medical professionals count pregnancy from the first day of the LMP because most women do not know the exact day they conceived. This means for the first two weeks of the "40 weeks," you aren't actually pregnant yet—your body is preparing for ovulation.

What if I have irregular cycles?

If your cycles vary significantly, calculation by LMP might be less accurate. In these cases, a "dating ultrasound" performed in the first trimester is considered the most reliable way to determine the due date.

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